Add-subtract binary counter circuit



Jan. 5, 1954 C. R. WILLIAMS ADD-SUBTRACT BINARY COUNTER CIRCUIT FiledAug. 18, 1950 AAAI -- 70 A/EX 7' S74 65 AAA! awn/1L6! /z. WILL/AMImar/24a 73/4! [we V Patented Jan. 5, 1954 ADD-SUBTRACT BINARY COUNTERCIRCUIT Charles R. Williams, Hawthorne, Galifl, assignor to NorthropAircraft, Inc., Hawthorne, Califi, a corporation of CaliforniaApplication August 18, 1950, Serial N 0. 180,255

6 Claims.

The present invention relates to cold cathode tube flip-flop circuitsadapted for use in binary counters, and is an improvement on the basiccircuit shown, described and claimed in the copending Hagen application,Serial No. 100,178, filed June 20, 1949.

Essentially a flip-flop is a device which has two stable states and iscapable of being triggered from one state to the other. A dual coldcathode as flip-flop tube has two conducting stable states; either onecathode is conducting, or the other cathode is conducting. The tube isnonoonducting only during relatively short transition times, andsuificient supply voltage is provided to insure refiring.

Circuits for use with dual cold cathode gas tubes to obtain flip-flopoperation have-the fol1owingelements in common:

1. A supply voltage source higher than the firing voltage of the tube.

2. A current limiting resistance in series with the supply voltage.

3. A cathodecircuit such that in either stable state the on cathode isat a higher positive potential than the off cathode.

4. A means of coupling in a triggering pulse which decreases the voltageacross the tube and extinguishes the glow current.

5. A means of maintaining the"on to off cathode difierential voltageduring the triggering transition time.

6. A means of delaying the rise of the voltage across the tube duringtriggering to allow ionization dissipation before refiring.

These components are shown, described and claimed in the Hagenapplication cited above.

In a multi-stage binary counter each flip-flop stage must be triggeredat exactly one-half the pulse repetition rate of the preceding stage.

One method of obtaining alternate carry pulses is to take them from theflip-flop cathodes in a suitable cathode circuit. Since the cathodesfire alternately, the one-half input rate is automatically obtained byviewing the output of only one of the cathodes.

'The on and off states of a binary flip-flop may be arbitrarily assignedand may be indicated by some device such as a glow lamp which lightswhen the flip-flop is on. Having assigned the on and off flip-flopstates, then for additive binary counting a carry pulse must be emittedfrom a particular flip-flop stage each time that stage changes from onto off. Conversely for subtractive counting a carry pulse must beemitted each time the stage changes from off. to

on. Thus, if additive-counting carry pulsesare derived from oneoathode,then subtractivecounting pulses may be derived from the other cathode.If both additive and subtractive carry pulses are generated, then it isnecessary to provide suit,- able gates which permit only one type or theother to pass at a given time.

It is an object of the present invention to pro.- vide a dual coldcathodetube cirouit-of the Hagen type, modified for binary counterruse,to generate both add and subtract carry pulses.

It is another object of the vpresentinvention to provide a simple binarycounting circuit using cold cathode glow tubes.

Briefly, the invention comprisesa flip-flop circuit using a dual coldcathode glow=tube,.together with circuit means, for shifting the glowdischarge from one cathode to the other under the control ofinputpulses. A carry pulse, output circuit is provided which generatesboth add and subtract carry pulses for the next stage, and means areprovided to block either type of carry pulse according toa control pulseinput. Thus, when the flip-flop circuitof-the present invention is usedin a multistage binary counter, itwill add or subtract the input pulsein accordance with a control pulse.

The invention will be more fully understood by reference to theaccompanying drawings in which:

Figure 1 is a side viewof a preferred form of cold cathode glow tubefor'use in the circuit of the present invention.

Figure 2 is a circular diagram illustrating the present invention in apreferred form.

Figure 3 is a series of wave form diagrams illu"- t-rative'oi how apositive pulse generated by a neon lamp, for example, is inverted andconveyed on as a negative carry pulse.

As :shown in Figure 1, the tube preferred for use in the circuits ofFigure -2 is-providedwith an envelope containing an anodewire:2,'flankedon one side by a cathode wire 3 and-flanked by a cathodewire tenths-other side. Thesewires pass through an external -pinch'5 toform an anode lead 6 and cathodeleads l and 8, respectively.

A preferred tube is oneinch long by -inoh inside diameter.The'gaspressure in the tube and the anode to cathode spacing is adjustedto give a desirable firing to burning voltage differential. Electrodesurface spacings of .030 inch in helium at250 mm. Hg-pressure; aresatisfactory, and cathode wires of,..0l0,to .015 in c;h

diameter .and 11 incniong wiltsatist ctor lmsrrr up to 1.0 ma. current.Suitable tube currents for flip-flop operation range from 0.1 to 1.0 ma.Such a tube will provide useable on to off cathode differentials of from50 to 150 volts. Burning voltages are about 150 to 200 volts and firingpotentials are about 250 to 500 volts depending upon gas mixture,material, and condition of cathodes.

For long life and most dependable operation, I prefer that the tube havefrom one percent to five percent of a recombinable polyatomic gastherein, such as hydrogen or water vapor, for example, in addition tothe noble gas filling, in accordance with the teachings of anothercopending Hagen et al. application, Serial No. 156,659, filed April 18,1950. The anode area is not critical, and conduction usually occurs fromrelatively small area points on the anode surface. The anode ispreferably placed centrally between the two cathodes to obtainsymmetrical electrical characteristics and in the same plane with thecathodes for ease of manufacture.

For ease of illustration, the tube of Figure l is shown in Figure 2 withthe anode entering the top of the tube. nected to a source of positivepotential +B through a limiting resistor I0, and is also connected toinput line II having a series input capacity I2 therein. Pulses to becounted are fed into the circuit through input line II.

Cathodes 3 and 4 are connected to ground through neon glow lamps I4 andI5, respectively, and through parallel cathode resistors I6 and I1,respectively.

Cathodes 3 and 4 are also connected to ground through differentialcapacitors I8 and I9, respectively, in series with shunt diodes and 2|,respectively.

Each respective junction of the differential capacitors I8 and I9, withtheir respective shunt diodes 20 and 2|, is grounded through pulseinversion capacitors 22 and 23, respectively, in series with inversiondiodes 24 and 25, respectively. The conduction direction of the shuntdiodes and the inversion diodes are reversed.

A blocking network B is provided with a midpoint M to which an outputline is connected; this output line being connected to the input line IIof a following stage similar in all respects to the counting portion ofthe circuit of Figure 2.

In order and in series outwardly, on the respective sides of midpoint Min the blocking network B, are output coupling capacitors 3| and 32,gate diodes 33 and 34, and output capacitors 35 and 36, the latter beingconnected to the respective cathodes 3 and 4 at the respective junctionsof pulse inversion capacitors 22 and 23 and the inversion diodes 24 and25.

An isolating resistor is connected from ground to the junction betweenisolation capacitor 3| and gate diode 33, and a corresponding isolatingresistance 4| is connected between isolation capacitor 32 and gate diode34 to ground.

An add bias line 42 is provided for all stages, and is connected to theblocking network B on one side of the midpoint M between the outputcapacitor 35 and the gate diode 33 through an add line resistor 43. Asubtract bias line 44 is provided, connected to the blocking network Bon the other side of the midpoint M between the output capacitor 36 andthe gate diode 34 through subtract line resistor 45.

In the operation of the circuit so far described, resistor I0 is thecurrent limiting resistor. Cathoderesistors IG-and I1, and capacitors I8and In Figure 2, anode 2 is con- I9 are used to maintain thedifferential voltage between cathodes 3 and 4 during the triggeringtransition times. Neon lamps I4 and I5 are used both to develop anoutput pulse, and to serve as indicators as to the conduction status ofcathodes 3 and 4; it is to be noted that neon lamps I4 and I5 by virtueof their characteristic of requiring a relatively high firing potentialvolts, for example) and of then returning to a substantially loweroperating potential (50 volts, for example) effect a useful positivepulse output without which the circuit herein disclosed would berendered effectively inoperative.

Shunt diodes 20 and 2| shunt out negative input pulses which wouldotherwise appear in the cathode circuits and act as carry pulses; shuntdiodes 20 and 2| do not attenuate the desired positive pulses generatedby the neon lamps I4 and I5. As these lamp-generated pulses arepositive. the diode capacity combinations 24, 22 and 25, 23 are used aspulse inverters so that only negative pulses are passed to the blockingcircuit 13 through pulse output lines 50 and 5|.

Figure 3 comprises a series of waveform diagrams illustrating hownegative pulses appearing at cathodes 3 or 4 are effectively shunted andhence do not appear on output lines 50 and 5| and how a positive pulsegenerated by neon lamp I4 or by neon lam I5 is inverted and conveyed onas a negative carry pulse. For example, assume a train of pulsescomprising waveform I is applied to input I I (Figure 2) whileconduction is taking place from anode 2 to cold cathode 4 of dual coldcathode gas tube I. First negative input pulse N1, cuts off conductionfrom anode 2 to cold cathode 4, it is during this time that negative pipN1 is effected in voltage level on cathode 4. N1 denotes an undesirednegative pip which appears on cathode 4 as a result of capacitancecoupling between the tube elements. Second negative input pulse N2 cutsoff conduction from anode 2 to cathode 3; cold cathode gas tube thenrefires, initiating conduction from anode 2 to cold cathode 4; it is atthis time that a second undesired negative pipe N2 is efiected in thevoltage level on cathode 4. Rising voltage level on cathode 4 effects arise in voltage across neon lamp I5 until a firing potential isattained; the voltage then drops sharply to a relatively constantoperational voltage level thus effecting a positive pulse P asillustrated in waveform II which appears at A in Figure 2. Thecombination of capacitor I! and diode 2! serves to differentiate andclip negative portion of waveform II, including negative pips N1 and N2,arising from capacitive coupling in input II, thus waveform III appearsat B (Figure 2); false carry pulses are therefore eliminated and onlypositive pulse P is applied to condenser 23 which, in conjunction withdiode 25, forms a difierentiating net-work. Diode 25 conducts during therise of pulse P1 of waveform III but blocks during the fall of pulse P1thus effecting negative spike P1 which appears on output line 5| i. e.waveform IV.

The foregoing discussion can be extended by similar analysis toconduction from anode 2 and to cold cathode 3.

In the blocking circuit B, isolating resistors 40 and 43, together withdiode 33, act as one gate, and on the other side of the midpoint Misolating resistors 4| and 45, together with diode 34, act as the othergate.

These gates, when supplied with the proper positive bias potential, willblock the negative output pulse appearing in pulse output lines 50 and5!. Thus, the blocking circuit B will pass an add or a subtract negativepulse into carry pulse line 38, in accordance with the application of apositive bias potential, to add bias line 42 or subtract bias line 44.

While there are many ways to apply the desired bias to bias lines 42 and44, we prefer to utilize a simple flip-flop of the Hagen type to operatethe bias lines 42 and 44 as further shown in Figure 2.

Here a Hagen type glow tube 59, similar to that shown in Figure 1, isconnected in a flip-flop circuit in which a limiting resistor fill isconnected to the anode 6i, and to a source of positive potential B+. Abias control input line 52 carrying negative pulses is also connected toanode 5|.

Cathodes B3 and 54 of tube 59 are connected to ground by respectivecathode resistors 65 and 66 bridged by cathode capacitors 6! and 68respectively.

The add bias line 42 is connected to one cathode 53 and the subtractbias line 44 is connected to the other cathode 64.

As negative pulses appear in the bias control input line E52, viacoupling capacitor 62a the glow discharge will flip from one cathode tothe other. When the cathode connected to bias line 42 or 44 is notinvolved in the glow discharge, no bias appears on that line. However,when the cathode connected to bias line 42 or M is operating, a positivebias will be imposed on that bias line. As this positive bias willcontinue as long as the particular cathode is energized, the countercircuit carry pulse line 30 will pass carry pulses of add or subtractcharacter in accordance with which cathode of glow tube 59 is involvedin the discharge. Accordingly, pulses applied to glow tube 59 willcontrol the output of the counter stage. As the add and subtract biaslines are connected to all of the counter stages, as indicated by biasline arrows ill, the entire counter will add or subtract pulses enteringcounter input line i I, in accordance with th condition of bias tube 59.

From the above description it will be apparent that there is thusprovided a device of the character described possessing the particularfeatures of advantage before enumerated as desirable, but whichobviously is susceptible of modification in its form, proportions,detail construction and arrangement of parts without departing from theprinciple involved or sacrificing any of its advantages.

While in order to comply with the statute, the invention has beendescribed in language more or less specific as to structural features,it is to be understood that the invention is not limited to the specificfeatures shown, but that the means and construction herein disclosedcomprise a preferred form of putting the invention into effect, and theinvention is, therefore, claimed in any of its forms or modificationswithin the legitimate and valid scope of the appended claims.

What is claimed is:

1. In an add-subtract multi-stage binary counter, a flip-flop circuitstage including a tube comprising an envelope, a pair of cold cathodesand an intermediate anode in said envelope, a filling of gas at glowdischarge pressure in said envelope, a limiting resistance, a source ofpotential higher than the firing potential of said tube connectedbetween said anode and both of said cathodes in series with saidlimiting resistance, an input line connected to apply an input pulse tosaid anode, a two-electrode glow tube connects ing each of said cathodesto the negative end of said potential source, an RC circuit connected toeach of said cathodes, a pulse inversion circuit means coupled acrossthe output of each of said cathodes, means for gating pulses generatedat one or" said cathodes, to obtain add carry pulses, and for gatingpulses generated at the other of said cathodes, to obtain subtract carrypulses, for the next flip-flop stage.

2. Apparatus in accordance with claim 1 including a crystal diodeshunting each of said cathodes to the negative end of said source,whereby negative pulses generated by said cathode circuits are preventedfrom passing to the output.

3. Apparatus in accordance with claim 1 wherein said pulse inversionmeans comprises a series capacitor and a rectifier across said cathodecircuit.

4. Apparatus in accordance with claim 1 wherein said means for gatingsaid output pulses comprises a crystal diode oriented in each of theoutputs from said pulse inversion means to pass pulses therefrom, andmeans for applying a potential bias to said crystal diode to blockpulses from passing to the output, said latter means including isolatingresistors across said crystal diode.

5. In an add-subtract multi-stage binary counter, a flip-flop circuitstage including a tube comprising an envelope, a pair of cold cathodesand an intermediate anode in said envelope, a filling of gas at glowdischarge pressure in said envelope, a limiting resistance, a source ofpotential higher than the firing potential of said tube connectedbetween said anode and both of said cathodes in series with saidlimiting resistance, an input line connected to apply an input pulse tosaid anode, a cathode circuit for each of said cathodes comprising atwo-electrode glow tube connecting said cathode to the negative end ofsaid source, and an RC circuit, a pulse inversion circuit means coupledto each of said cathode circuits, a crystal diode coupled to each ofsaid pulse inversion circuits, an add bias line, a subtract bias line,bias isolating resistors connecting said bias lines to the cathode endsof said crystal diodes, isolating resistors connecting the plate ends ofsaid crystal diodes to the negative end of said source, a dual coldcathode control flipfiop, a bias control input line connected to applypulses to trigger said control flip-flop, said add bias line connectedto one cathode and said subtract line connected to the other cathode ofsaid control flip-flop.

6. A plurality of flip-flop circuits stages as recited in claim 5wherein said add and subtract bias lines are similarly connected to eachof said stages, whereby, dependent on the state of said controlflip-flop, all of the stages carry pulses generated on one or the otherof said cathodes.

CHARLES R. WILLIAMS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,462,275 Morton et a1 Feb. 22, 1949 2,537,427 Seid et al Jan.9, 1951 OTHER REFERENCES The Binary Quantizer, Barney, ElectricalEngineering, November 1949; pages 962-967.

